Monarch

Danaus plexippus plexippus (Linnaeus, 1758)

Adult ventral photo (Click to enlarge)

Adult photo (Click to enlarge)

Adult photo (Click to enlarge)

Ohio county distribution

Flight period (Temporal distribution)

STATUS: Regular immigrant; common.

DISTRIBUTION/RANGE: This species occurs throughout North and South America and has established permanent populations in Hawaii and Australia. In North America, D. plexippus is a permanent resident only in southern Florida, southern California, and Mexico. Ohio specimens are primarily the result of annual migrations northward from central Mexico. This species has been recorded from all 88 Ohio counties (see map).

HABITAT: This species occurs in virtually any open habitat. Typical habitats include old fields, roadsides, prairie remnants, gardens, and urban yards.

HOSTPLANT(S): In Ohio, this species has been found and reared on common milkweed. Larvae have also been found on swamp milkweed and butterfly-weed. Milkweeds are the primary hosts of this butterfly.

FLIGHT PERIOD: Two to four overlapping generations, depending on how early in the season this species becomes established (see graph). Extreme dates range from 5 May to 9 November.

SIMILAR SPECIES: The Viceroy (Limenitis archippus). This species can also be confused with the Queen (D. gilippus), but the orange ground color of D. plexippus will separate it from the much darker brown D. gilippus.

GENERAL COMMENTS: This is probably the most familiar butterfly in the State, and is a common sight in open areas in late summer and early autumn. This is also Ohio's only species which migrates both north and south annually. Each autumn, this species participates in mass migrations, with adults gathering in numbers as they head southward to their overwintering grounds in Mexico. These migrations involve non-reproducing adults from the entire northeastern United States and Canada. Although many adults travel alone, occasionally aggregations are formed. The largest migratory aggregation on record for Ohio occurred in September 1892, when millions of individuals descended into Cleveland from Canada (Webster, 1892; 1912; Anonymous, 1893). This migration coincided with an epidemic of cholera, and many people who witnessed this aggregation believed that the butterflies were disguised cholera germs (Anonymous, 1892). Another large aggregation occurred over Cleveland in 1872 (Saunders et al, 1875).

Today, large gatherings of migrating adults still occur on the Lake Erie Islands, especially Kelleys Island. These individuals apparently gather on the islands to rest and feed after crossing Lake Erie from Canada. The number of individuals arriving on the islands vary considerably from year to year (Teraguchi, 1988). Aggregations apparently move quickly through the State. One aggregation, noted in Seneca County on 3 October 1907 (Henninger, 1910), was observed in Pickaway County the next day (Bales, 1907). Bales noted that this aggregation moved steadily from north to south, and estimated that millions of individuals were involved. Although the majority of Ohio monarchs may eventually reach the overwintering grounds in the mountains of central Mexico, some individuals may pass the winter in southern Florida, or on the Caribbean Islands.

After reaching Mexico, adults gather by the millions in small areas where winter temperatures are slightly warmer than in surrounding habitats. Adults roost on trees and on each other, creating huge forests of orange. Throughout the winter months, the monarchs remain fairly inactive, and only fly about in search of water and, if it can be found, nectar. During this period, adults are in reproductive diapause, primarily existing upon fat reserves that had been accumulated during the larval stage. Many adults die during this period, usually from predation and lethal cold temperatures. As their fat reserves are used up, their reproductive systems begin to develop, and adults become more active. During late winter-early spring, the adults mate and begin to fly northward. It is estimated that less than one percent of the original adults survive to return to northern areas (Opler and Krizek, 1984). As the females fly northward, they search for milkweeds upon which to lay eggs. The overwintering females usually do not survive for long and it is doubtful that overwintering females ever return as far north as Ohio. It is their offspring that complete the cycle and find their way into Ohio. Because northward flying adults fly as solitary individuals, few people notice this phase of the migration.

Because the monarch depends on its overwintering grounds for survival, any factor which might disturb the suitability of this limited area could have a dramatic impact on this butterfly. Until recently, the overwintering grounds in Mexico had been threatened by lumbering, but with the realization that the area had unique tourism potential, the Mexican government has since protected the sites. However, these sites may still be adversely affected by the pressure of tourism. Further study of the potential impacts of this activity needs to be undertaken. Thus, the status of the monarch in Ohio depends heavily upon the conservation of the overwintering grounds in Mexico.

In 1938, a program of tagging monarchs was initiated by Fred A. Urquhart of Toronto, Canada (Urquhart, 1960). This method of identifying individuals, using identification tags attached to their wings, ultimately led to the discovery in 1975 of the famous overwintering grounds in central Mexico (Urquhart, 1976). This program of tagging is still in progress across North America and includes several sites in Ohio. A number of specimens tagged in Ohio have been recovered and at least two specimens tagged on Kelleys Island in 1983 were later observed in Texas and at Angangueo, Michoacan, Mexico. (Sonja E. Teraguchi, pers comm, 1983; Urquhart, 1960).

The larvae of this species feed on milkweeds, which usually possess poisons known as cardiac glycosides. These chemicals, which are extremely toxic to most vertebrates, are incorporated into the bodies of the larvae and adult monarchs. In addition to the glycosides, monarchs sequester emetic substances which cause vomiting in birds. Thus, birds which eat monarchs do not die, but only become ill. Birds which eat monarchs generally remember the experience as a bad one, and as a result the monarch gains a certain amount of protection from predation. The bright color patterns found on larval and adult monarchs are thought to be aposematic. These easily recognized patterns serve as warnings which are quickly learned by potential predators, because they can associate the striking appearance of this insect with the bad experience of eating one.

The monarch forms a model for the viceroy (Limenitis archippus) in probably the most famous example of Batesian mimicry. In this relationship, the adult viceroy (the mimic) has evolved a very similar color pattern to that of the distasteful monarch. By resembling the monarch, the viceroy gains protection from predators who have tasted monarchs and cannot distinguish between the two butterflies. However, an intriguing study (Ritland and Brower, 1991) challenges this theory by concluding that A. archippus is also distasteful, suggesting that this species is a Mullerian co-mimic of D. plexippus, rather than a Batesian mimic.

The flight of the monarch is very slow and leisurely, and is characterized by long periods of gliding. Only when alarmed does this species exhibit a very rapid flight. Males patrol while searching for females, and will chase after most other large orange butterflies. Adults are avid flower visitors, and feed with the wings together or outstretched. This species is not very wary, and can usually be very closely observed. Roosting adults hang upside down from plants at night.